Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$62.49	8.388%	$67.7317	$67.73	$67.75	$67.70
Purchase #2	$133.68	12.422%	$150.2857	$150.29	$150.30	$150.30
Purchase #3	$75.66	12.715%	$85.2802	$85.28	$85.30	$85.30
Purchase #4	$65.49	9.753%	$71.8772	$71.88	$71.90	$71.90
Purchase #5	$36.70	9.553%	$40.206	$40.21	$40.20	$40.20
Purchase #6	$91.44	12.763%	$103.1105	$103.11	$103.10	$103.10
Purchase #7	$79.45	8.121%	$85.9021	$85.90	$85.90	$85.90
7 purchase totals =	$544.91		$604.3934	$604.40	$604.45	$604.40